Dark matter 'bridge to nowhere' found in cosmic void

Published: Tuesday, September 16, 2008, 15:09 [IST]

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London, September 16 : New observations from the 40-inch Wise Observatory telescope in Israel has revealed more than a dozen galaxies lined up along a bridge of dark matter inside a region of nearly empty space, which is being called as 'bridge to nowhere' by astronomers.

According to a report in New Scientist, this 'bridge to nowhere' could shed light on how small galaxies formed in the early universe.

Galaxies in the universe are arranged in a lacy structure that contains many holes, or voids, that are largely bereft of galaxies.

But, the voids are not completely empty; astronomers expect they are criss-crossed by filaments of dark matter.

Now, astronomers have found a total of 14 galaxies that appear to be part of a dark matter bridge at least 1.5 million light years long.

The string of galaxies spans just 0.5 per cent of a 'mini-void' - a region of space containing mostly dim, dwarf galaxies kept small by their relative isolation from other matter.

But, the underlying dark matter bridge may be far longer than that.

All of the galaxies are small dwarfs that seem to be unrelated. But, Adi Zitrin and Noah Brosch of Tel Aviv University in Israel noticed that they all seemed to be arrayed in a line.

Further study revealed that after more than a billion years of inactivity, all of the galaxies began forming stars again less than 30 million years ago.

That was unexpected, since new star formation often occurs when galaxies interact, and these seem to be keeping to themselves. Nearby galaxies, for example, did not seem to have more star formation than those lying farther away.

"This is a strange thing," Brosch told New Scientist. "A priori, one would not expect galaxies that have nothing to do with each other, a few million light years apart, to make stars at the same time," he added.

That synchronization seems to suggest that the galaxies have come into contact with new, star-forming material, like a passing cloud of gas.

Ordinarily, the gas would be too tenuous to condense down and cause a new burst of star formation.

"But if a swath of dark matter is connecting the galaxies, its gravity could help concentrate the material," said Brosch.

If the galaxies are pinned to a filament of dark matter, further study could help illuminate how star formation occurred in the early universe, he added.

That's because the first galaxies are thought to have gotten their start when gas accumulated around denser regions of dark matter.

Solidifying the case for a filament might be possible by observing objects lying behind the void.

According to John Huchra of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, if their light is bent travelling through the void, the gravitational effect of unseen dark matter could be to blame.